A conventional boot of this type as shown in FIG. 1 is known (hereinafter referred to as "prior art A"). More specifically, a tubular elastic body 4, formed integrally with one end of a boot 3 and having one closed end, is received in a holder member 2. One end portion of the guide pin 1 is received in the elastic body 4, and the guide pin 1 is disposed in sliding contact with the elastic body 4 over the entire circumference of the guide pin 1, so that the guide pin 1 is borne or supported by the holder member 2 through the elastic body 4. With this arrangement, the boot 3 serves to damp the end portion of the guide pin 1 and also to seal this end portion.
Another conventional boot as shown in FIG. 2 is also known (hereinafter referred to as "prior art B"). A bearing member 5 for supporting a guide pin 1 is fitted in an annular groove 16 formed in an inner peripheral surface of a holder member 2. The bearing member 5 is disposed separately from the boot 3. A ring-shaped flange 6 is fitted in an annular groove 17 formed in the outer peripheral surface of one end of the holder member 2.
There is known a further conventional boot as shown in FIG. 3 and disclosed in Japanese Laid-Open (Kokai) Patent Application No. 35861/76 (hereinafter referred to as "prior art C"). A flange 8 of the boot 3 made of an elastic material is fitted in an annular groove 7 formed in an inner peripheral surface of an end of a boss of a caliper 10. The flange 8 fits on a guide pin 1, and the guide pin 1 is received in the caliper 10 acting as a holder member for the guide pin 1. That portion of the flange 8 disposed in sliding contact with the guide pin 1 serves as a bearing portion so as to perform a damping function. The outer peripheral portion of the flange 8 fitted in the annular groove 7 in the boss 2 is compressed between the bottom of the groove 7 and the outer periphery of the guide pin 1 to thereby provide a seal. Thus, the flange performs both the damping function and the sealing function.
FIG. 5 shows a disc brake incorporating a conventional boot 3 formed of an elastic material secured to a boss of the support member 18 and the guide pin 1 fixedly secured to the caliper 10 and a brake disc 17.
In the prior art A shown in FIG. 1, however, the guide pin 1 is mounted in the holder member 2 in such a manner that the end portion of the guide pin 1 is disposed in sliding contact with the elastic body 4 over the entire circumference of the guide pin 1. Therefore, this mounting operation cannot be carried out easily. With respect to the prior art B, since the bearing member 5 for performing the damping function is disposed separately from the flange 6 of the boot 3, the mounting operation of these members as well as the mounting operation of the guide pin 1 in the holder member 2 cannot be carried out easily. As regards the prior art C, the flange 8 of the boot 3 is fitted in the annular groove 7 in the inner peripheral surface of the end of the boss 2 of the caliper 10 (which caliper acts as the holder member and receives the guide pin 1 therein), so that the flange 8 can perform both the damping function and the sealing function. However, such is not proper. Particularly when the outer peripheral portion of the flange 8 formed of an elastic material fitted in the annular groove 7 is compressed by the bottom of the groove 7 as shown in FIG. 4, the outer peripheral surface of the flange 8 is not disposed in intimate contact with the bottom of the groove 7, thus failing to provide a satisfactory sealability.